(a) Which of the ions K+
, Na+
, Be2+
will have the largest heat of hydration? Which the smallest?
(b) Of the two compounds KNO3
and NaNO3
, which has the stronger intermolecular forces?
(c) Of the two compounds PCl3
and Xe, which has the stronger intermolecular forces?
(a) The heat of hydration of an ion refers to the energy released or absorbed when an ion is surrounded by water molecules and solvated. Generally, smaller ions with higher charge have stronger attractions to water molecules, leading to a larger heat of hydration. Therefore, Be2+ will have the largest heat of hydration, followed by Na+ and then K+.
(b) The strength of intermolecular forces in a compound is influenced by factors such as molecular size, shape, and polarity. In the case of KNO3 and NaNO3, both compounds have similar molecular structures, composed of ions K+/Na+ and NO3-, and similar polarities. Consequently, the intermolecular forces in both compounds will be primarily ionic forces. Since potassium ion (K+) has a larger charge compared to sodium ion (Na+), KNO3 is expected to have slightly stronger intermolecular forces than NaNO3.
(c) PCl3 is a compound composed of polar molecules, while Xe is a noble gas that exists as individual atoms. Intermolecular forces in compounds are generally stronger than those between noble gas atoms. Therefore, PCl3 will have stronger intermolecular forces compared to Xe.
(a) To determine which ion will have the largest and smallest heat of hydration among K+, Na+, and Be2+, we need to consider their charge and size. Generally, ions with higher charge and smaller size have stronger interactions with water molecules, resulting in a larger heat of hydration.
To compare the sizes:
- K+ and Na+ both have a +1 charge, but Na+ is smaller than K+ due to the larger nuclear charge. Therefore, Na+ will have a stronger attraction to water molecules and a larger heat of hydration compared to K+.
- Be2+ has a +2 charge, which is higher than the +1 charge of both K+ and Na+. Additionally, Be2+ is smaller in size due to the increased nuclear charge. Therefore, Be2+ will have the largest heat of hydration among the three ions.
So, in summary, the largest heat of hydration will be for Be2+, followed by Na+, and finally K+ will have the smallest heat of hydration.
(b) To determine which compound, KNO3 or NaNO3, has stronger intermolecular forces, we need to consider their molecular structures and the nature of the interactions present.
Both KNO3 and NaNO3 are ionic compounds and consist of positively charged ions (K+ or Na+) and negatively charged ions (NO3-). In these compounds, the intermolecular forces are due to the attraction between opposite charges.
However, the strength of the intermolecular forces primarily depends on the charges and sizes of the ions. Since K+ has a higher charge (+1) compared to Na+ (+1), and potassium ions are larger in size compared to sodium ions, KNO3 will have stronger intermolecular forces compared to NaNO3.
Therefore, KNO3 has stronger intermolecular forces than NaNO3.
(c) To determine which compound, PCl3 or Xe, has stronger intermolecular forces, we need to consider their molecular structures and intermolecular forces involved.
PCl3 is a polar molecule due to the presence of a lone pair on phosphorus, resulting in a dipole moment. It exhibits dipole-dipole interactions between its polar molecules.
On the other hand, Xe is a noble gas and exists as individual atoms, which do not form molecules. Noble gases are known for their weak intermolecular forces such as London dispersion forces.
In comparison, dipole-dipole interactions in PCl3 are generally stronger than London dispersion forces in Xe. Therefore, PCl3 will have stronger intermolecular forces compared to Xe.